The epidermal growth factor receptor (EGFR) regulates proliferation, migration, apoptosis, and differentiation of cells. Many types of cancer have abnormally high EGFR activity that contributes to their growth, and studies have shown that inhibiting EGFR can reduce tumor size. We made diacylglycerol kinase (DGK) delta knockout mice and discovered that by regulating protein kinase C enzymes, DGKdelta modulates the expression and activity of EGFR. This proposal has three aims that will help us understand how DGKdelta regulates EGFR signaling and will test the potential anti-tumor effects of disrupting the function of DGKdelta. In Aim 1, we will determine how DGKdelta modulates EGFR expression. We found enhanced EGFR ubiquitination and increased PKC activity in DGKdelta deficient cells. Additionally, we discovered that PKCalpha is required for proper EGFR ubiquitination. Together, these data led us to hypothesize that DGKdelta regulates EGFR ubiquitination through PKCalpha. We will test this possibility in Aim 1. We also discovered that DGKdelta modulates EGFR activity independently of changes in EGFR expression. In DGKdelta deficient cells and tissues, we found enhanced phosphorylation of a threonine residue in EGFR. This phosphorylation is known to inhibit EGFR activity and our data indicate that PKCdelta is responsible. This led us to hypothesize that DGKdelta regulates EGFR activity by inhibiting PKCdelta phosphorylation of EGFR. In Aim 2, we will test this possibility. Finally, in Aim 3, we will use cell culture and mouse xenograft models to test the impact on tumorigenesis of disrupting the function of DGKdelta. Collectively, our experiments will clarify how DGKdelta regulates EGFR signaling, will define the contribution of DGKdelta to tumor formation, and will measure the anti-tumor effects of disrupting the function of DGKdelta. PUBLIC HEALTH RELEVANCE: EGFR is an important cancer target. We have found a novel way to regulate its expression and activity. These properties of EGFR are fundamentally important for it to promote cancer and our experiments might uncover new anti-cancer therapies. Thus, our proposal has important relevance to public health.